This invention relates to a magnetic disc apparatus of contact-start-stop type.
Generally, in a magnetic disc apparatus, even after a motor power source is turned off, the disc is not stopped immediately but continues to rotate at a gradually decreasing speed because of the inertia of rotatory bodies such as the disc, spindle and motor. If the disc is rotated at a low speed in a magnetic disc apparatus of contact-start-stop type, a head abuts against the disc surface and continues to rub on it. Accordingly, various types of braking operations are employed to decrease the period through which the head rubs on the disc surface, for the purpose of extending the lifetime of the apparatus. Among them, there are:
(A) APPLYING A MAGNETIC FIELD ACROSS AN ALUMINUM DISC SECURED TO THE SPINDLE TO GENERATE EDDY CURRENTS IN THE ALUMINUM DISC FOR EFFECTING BRAKING OPERATION;
(B) ABUTTING AN ELECTROMAGNETICALLY CONTROLLED ARMATURE DISC AGAINST A BRAKE DISC FOR EFFECTING BRAKING OPERATION; AND
(C) CUTTING OFF THE MOTOR DRIVE POWER SOURCE AND THEN APPLYING A D.C. current to the motor winding for effecting braking operation.
When the above three measures are relied upon, problems still remain since power is externally supplied in many applications to a small capacity apparatus. The measures (a) and (b) set forth above wherein power is supplied for effecting the braking operation following cutting off of power source for motor drive require a sequential control for the power source and in additon, lose the power supply for effecting the braking operation in the event of an emergency such as power failure. Even in the measure (b), the brake is placed into operation concurrently with cutting off of power source for motor drive so that a brake shoe rubs on an armature while the disc is rotating at a normal high speed (usually about 3000 r.p.m.), resulting in wear of both the brake shoe and the armature.